The present invention relates in a general way to rotating electric machines.
More precisely, the invention relates to rotating machines of the alternator or alternator/starter type, which are employed in motor vehicles.
And yet more precisely, the invention relates to the rotating machines the rotor of which comprises permanent magnets as well as one or more excitation coils.
Such rotating machines are said to have compound excitation; the excitation of the coil or coils placed in the rotor, driven by a suitable electrical power supply, makes it possible to strengthen or reduce the power delivered by the machine (the sign of the electrical power supply delivered to the excitation coils possibly being reversed).
These compound-excitation machines thus make it possible to enhance the effectiveness of the machine and its flexibility of use.
An example of such a machine is disclosed by the document EP 741 444. The rotor more particularly set out in FIG. 5 of this document has a claw-type structure comprising magnetised parts, and an annular excitation coil placed around the rotational shaft of the machine.
It is also known to make up the rotor of a rotating machine not by imbricating claws some of which would be magnetised, but by the stacking, parallel to the rotational axis of the machine, of sheet-metal plates cut out beforehand according to the same contour, the said common contour of the metal plates defining housings intended to receive permanent magnets. EP 803 962 discloses an example of such a rotor.
This latter configuration, by comparison with the claw-type configuration, offers the advantage of producing uniform lines of magnetic field along the axial direction of the machine, which is not really the case with a claw-type rotor. And this arrangement enhances the efficiency of the machine.
However the rotor of EP 803 962 does not have compound excitation, which limits the flexibility of this machine in use.
A first aim of the invention is to make it possible to produce a rotating machine combining the advantages of the two types of machine set out above.
Furthermore, in the case of the machines in which the rotor comprises one or more excitation coils, the application of voltage to the said coils may cause them to heat up, which would impair safety and the efficiency of the machine.
A second aim of the invention is furthermore to ensure safe and efficient operation of the rotating machine, avoiding any excessive heating of elements such as excitation coils.
In order to achieve these aims, the invention proposes a rotating electric machine, especially an alternator or alternator/starter for motor vehicles, including a stator surrounding a rotor equipped with a pack of metal plates, a gap between the stator and the rotor, permanent magnets integrated into the rotor and excitation coils integrated into the rotor, in which the excitation coils are wound around salient poles cut out in the pack of metal plates of the rotor, and the permanent magnets are accommodated in housings formed in the pack of plates of the rotor, characterised in that the housings are closed axially at each of their ends by a retaining piece equipped with a non-magnetic part intended to come into abutment with the magnets, and in that the retaining piece features recesses for accommodating buns of the excitation coils.
Preferred, but non-limiting, aspects of the machine according to the invention are as follows:
the retaining piece, at its outer periphery, features axial extensions directed in the reverse direction with respect to the pack of plates of the rotor and shaped to retain the excitation coils counter to the action of centrifugal force,
the end part of the said extensions is inclined towards the rotational axis of the machine,
the said extensions have a pointed shape, such as trapezoidal,
the said extensions are carried by a ferromagnetic cap which has the same shape as the plates, the said cap being interposed between the pack of plates and a non-magnetic flange, the cap and the flange constituting the retaining piece (13),
means for cooling the coils are provided,
the said cooling means comprise fan blades,
the blades are shaped to create a radial airflow and an axial airflow,
the blades are of different sizes,
the retaining piece carries fan blades between the excitation coils, and the blades extend in projection from the retaining piece,
the blades are of a single piece with the retaining piece,
the blades are attached to the retaining piece,
the surface of the retaining piece features bosses for holding the blades,
the flange features holes for fixing the blades,
grooves are provided on the surface of the flange for accommodating a wire of the excitation coils when the said wire passes from one coil to the other, and
at least one groove is intersecting,
the housings of the permanent magnets are open towards the outer periphery of the rotor,
the housings of the permanent magnets are closed at the outer periphery of the rotor as described, for example, in the document U.S. Pat. No. 6,147,429.